Dual targeting GLI1 and EZH2 for treatment of invasive breast cancer

About 12% of breast cancers are invasive breast cancers, including triple-negative breast cancer (TNBC), which manifests early metastasis and recurrence with limited treatment options. Therefore, there is an urgent need to better understand key mechanisms governing invasive breast cancers to develop effective treatment strategies. Our clinical database analysis indicates that overexpression of EZH2 is often correlated with metastatic breast cancer, and high expression of the oncogenic GLI1-Hedgehog signaling is positively correlated with poor survival of invasive breast cancers. Our pilot findings indicate that deletion of the EZH2 gene results in reduced expression levels of GLI1 and its downstream target gene, cyclin D1. Previous literature also suggests that cMYC can activate GLI1, and the EZH2-cMYC complex can induce target gene expression in an atypical manner, promoting cancer. However, it is reported that the clinical use of either an EZH2 inhibitor alone or a GLI1 inhibitor alone cannot hinder tumor growth or metastasis. Our data suggest that EZH2 may regulate GLI1 expression, but its synergistic functionality has not been fully elucidated. We expect that EZH2 forms a complex with cMYC and GLI1 to synergistically activate the target genes involved in breast cancer progression (for example, GLI1 and Cyclin D1). As a result, a combination of EZH2 inhibitors and GLI1 inhibitors can synergistically suppress cancer cell growth and metastasis, serving as a new and effective therapeutic option for invasive breast cancers. Using a cell viability assay, the combination therapy was shown to be more effective in inhibiting TNBC cell viability compared to the single-drug treatment and the vehicle groups. The wound healing assay showed that combination therapy was more effective in suppressing TNBC cell migration. The CompuSyn for drug synergy analysis, both the Combination Index (CI) and Dose Reduction Index (DRI) indicated that the combination therapy exhibited significant synergistic effects, where Vismodegib could reduce the dose by ~52-fold, while GSK126 could reduce the dose by ~22-fold. Form the findings, we believe that dual targeting GLI1-EZH2 has potential to become a novel and effective combination treatment for invasive breast cancer in the clinical setting.